Extraction is an important chemical separation technique, possessing advantages such as high target selectivity, good adaptability to various materials, low energy consumption, easy to operate, and easy to achieve large-scale continuous production. Extraction can be widely used in chemical industry, metallurgy, new energy field, bio- and medical engineering, environmental engineering, natural product extraction, preparation of new materials and the efficient utilization of resources, etc., thus is known as “the most promising green chemical separation technology in 21st century”. With the separation objects and separation systems become increasingly complex, the traditional liquid-liquid two-phase extraction technique and the apparatus do not meet the requirement in emerging chemical separation system. Most of the structure designs of the extraction and separation apparatus in prior art aim at the liquid-liquid two-phase extraction process, and are divided into two types according to their mass transfer characteristics and phase separation process requirements, namely sequential contact and continuous contact extraction equipments, e.g. the mixer-settler extraction tank, the dial extraction tower, and the vibration sieve tower, etc. For some multi-component complex systems and easy emulsifying systems, disadvantages such as low selectivity, lengthy separation steps, and low separation efficiency lie in the traditional liquid-liquid two-phase extraction process, and disadvantages such as complex design of the flow direction and cascade structure, difficulties in effectively controlling of the interphase mass transfer and phase separation processes of the complex system, and high cost in operation and maintenance also lie in the apparatus. Taking biochemical system separation as an example, the cost in separation steps always constitutes more than 80% in the entire production costs. The serious lagging in separation apparatus development becomes the bottleneck problem that restricts the progress in our chemical process engineering field.
Liquid-liquid-liquid three-phase extraction is a newly emerged technique with high selectivity developed from microemulsion phase extraction technology to enhance mass transfer and separation based on the interface effect in the extraction process. Starting from the regulation of the micro-nano phase structural interface characteristics of the separation medium, one-step extraction and simultaneous three-phase separation or grouping separation of multiple target components in complex systems can be realized by controlling phase formation and separation behavior of three macroscopic co-existed liquid phases with different structures and properties. For separation of biochemical products such as penicillin, lincomycin, glutamic acid fermentation broth, the Chinese Patent ZL 00107655.8 provides a three-liquid-phase extraction system, consisting of an organic phase, a polymer phase, and a rich brine phase, to realize three-phase extraction and separation of different target extracts in the rich brine phase. The phase formation behavior in this new three-phase extraction system is easy to control comparing to other three-liquid-phase extraction system types, and the allocation behavior of different target extracts among the three macroscopic co-existed liquid phases can be effectively controlled by the phase formation behavior of the three-phase system. Applying this three-phase extraction technique to penicillin fermentation broth treating, target extraction, purification, and impurity removing process can be realized by one step, and intermediate steps such as demulsification, lyophilization and discoloration can be omitted and the process is simple. Due to high selectivity, the impurity and byproduct separation efficiency, the yield and purity of target product in three-phase extraction are significantly higher than that in traditional two-phase extraction technique. Currently, three-phase extraction separation in complex multi-component system becomes a hotspot and frontier topics in related fields internationally, and breakthroughs have been achieved in three-phase extraction basic theory and technique research. However, industrial applications of three-phase extraction new techniques are not achieved due to lack of industrial apparatus adapted to three-phase continuous extraction technique.
In order to take the advantages of liquid-liquid-liquid three-phase extraction technique for separation of complex multi-component systems, a series of three-phase extraction apparatus that meet the three-phase extraction technical features and process requirements have been developed. The Chinese Patent ZL 00107700.7 introduces a series-wound self-pumping multi-channel phase dispersion extraction apparatus, which is suitable for a three-phase extraction system consisting of an organic solvent and polymer-based aqueous two-phase extraction system. By using a self-pumping stirrer, effective control of mass transfer among any two of the three liquid phases and phase dispersion in the three-phase extraction system is realized for the first time, and emulsification in the extraction process can be effectively avoided. However, the extraction operation cannot be continuous and the device processing power is limited, not suitable for the industrial continuous production. The Chinese Patent ZL 02106742.2 provides a liquid-liquid-liquid three-phase continuous extraction vibration sieve tower. This apparatus resolves the problem about how to perform continuous extraction operations. However, the flow directions of the three flows in the three-phase system and the countercurrent operations of the three liquid phases cannot be effectively controlled due to the structure design of the tower separation device. In addition, the mass transfer efficiency and separation parameters are still low, the operating conditions are harsh, flooding and axial backmixing are easy to happen, and scaling-up process is difficult. In fact the apparatus is an integrator of two liquid-liquid two-phase extraction-tower units being connected together in series in order to realize contacting and mass transferring between any two phases of three-liquid-phase flow. The interphase mass transferring is not carried out in a manner of three-liquid-phase process, and the flow behaviors of the three liquid phases are not controllable. To solve the above problems, the Chinese Patent ZL 02121210.4 suggests a liquid-liquid-liquid three-phase horizontal continuous stirring extraction apparatus. This apparatus for the first time realizes the liquid-liquid-liquid three-phase continuous in-situ contact mass transfer, with advantages such as reduced backmixing, high theoretical stages, high extraction efficiency, simple structure, easy to scaling up, continuous operation, low energy consumption, low room occupation, and easy to retain steady state operation, suitable for the three-phase extraction and separation process of easy emulsified biochemical products. However, this apparatus cannot realize multi-stage continuous and countercurrent extraction operation, the three main phases cannot mix well, and the mass transfer happens only at the phase-to-phase contact surface, with low processability, complicated device structure and difficulties to scale up. Therefore, the Chinese Patent CN200910090899.X suggests also a liquid-liquid-liquid three-phase continuous extraction mixer-settler apparatus. This apparatus solves the problem of how to control the three flow directions in the three-phase extraction system, and multi-stage series-wound continuous extraction operations can be conducted. However, this apparatus does not design the device structure from the essential characteristics of the phase formation behavior in the three-phase extraction system. The extraction and separation operations are based on quick phase separation of the three liquid phases, and the countercurrent operation combinations of any two of the three liquid phases are not realized, thus the process requirement of controlling the mutual mass transfer and distribution among the three liquid phases in the three-phase extraction process are not satisfied. Deutsch Bayer Co. suggested a multi-stage three-phase extractor (Chinese Patent ZL 96197714.0) to meet the requirement of countercurrent and continuous operations of three-liquid-phase extraction process. However, a precondition for this apparatus design is the three liquid flows in the three-phase system can not be miscible during the course of phase-mixing and contacting. Two phases in the three-phase system are used as dispersion phase and the other phase is served as continuous phase to flow countercurrently. This apparatus solves the problem of co-current or countercurrent between the continuous phase and the first or second dispersion phase. However, for a three-phase system consisting of an organic phase, a polymer phase, and a rich brine phase, the phase formation behavior in the three-phase system is to form a aqueous two-phase extraction system by the polymer phase and the rich brine phase to transfer the target mass from the rich brine phase (the bottom phase) to the polymer phase (the middle phase), followed by the target mass transfer from the polymer phase (the middle phase) to the organic phase (the top phase) by mixing the aqueous two-phase extraction system with the organic phase. The prerequisite of the formation of a stable three-phase system is the phase formation of the aqueous two-phase system of polymer phase-rich brine phase. The mass transfer behavior in the three-phase system is closely related to the phase formation behavior. This apparatus cannot realize effective control of the phase formation behavior of the three-phase system consisting of an organic phase, a polymer phase, and a rich brine phase, as well as of the phase type of the dispersion and continuous phases.